Geologic description
The Silver Queen Mine was discovered in 1887 and operated intermittently until 1911 (Buddington and Chapin, 1929). It has 2,600 feet of workings, 500 feet of connecting raises, and at least 4 adits. The Silver Queen and geologically similar Glacier mines (JU173) were connected in 1903 (Spencer, 1906). By 1891, the combined production from the two mines was 19,300 ounces of silver and 41 ounces of gold. The U.S. Bureau of Mines estimated that they produced nearly $500,000 worth of silver and gold at 1903 prices (Redman and others, 1989). The Silver Queen veins were mined for 900 feet along strike and over a 400-foot vertical extent. The Silver Queen deposit consists of several boudinaged, concordant, quartz-calcite veins along the contact between black phyllite and green phyllite (Redman and others, 1989). The veins vary from single veins that average about 2 feet thick, to stringers. They contain arsenopyrite, chalcopyrite, galena, native gold, native silver, pyrargyrite, pyrite, pyrrhotite, sphalerite, tetrahedrite and rare stibnite. The U.S. Bureau of Mines samples of the veins contained up to 1,076 ppm silver, 14.3 ppm gold, 0.62 percent lead, 0.68 percent zinc, and 0.10 percent copper. One sample contained 509 ppm tungsten (Redman and others, 1989). This mine is in the Juneau Gold Belt, which consists of more than 200 gold-quartz-vein deposits that have produced nearly 7 million ounces of gold. These gold-bearing mesothermal quartz vein systems form a zone 160 km long by 5 to 8 km wide along the western margin of the Coast Mountains. The vein systems are in or near shear zones adjacent to west-verging, mid-Cretaceous thrust faults. The veins are hosted by diverse, variably metamorphosed, sedimentary, volcanic, and intrusive rocks. From the Coast Mountains batholith westward, the host rocks include mixed metasedimentary and metavolcanic sequences of Carboniferous and older, Permian and Triassic, and Jurassic-Cretaceous age. The sequences are juxtaposed along mid-Cretaceous thrust faults (Miller and others, 1994). The sequences are intruded by mid-Cretaceous to middle Eocene plutons, mainly diorite, tonalite, granodiorite, quartz monzonite, and granite. Sheetlike tonalite plutons emplaced just east of the Juneau Gold Belt and undeformed granite and granodiorite bodies that are emplaced farther to the east are between 55 and 48 Ma (Gehrels and others, 1991). The structural grain of the belt is defined by northwest-striking, moderately to steeply northeast-dipping, penetrative foliation that developed between Cretaceous and Eocene time (Miller and others, 1994). The majority of the veins in the Juneau Gold Belt strike northwest. Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997). |
